1. Field of the Invention
The present invention relates to methods and systems for selectively disconnecting a power generation source, such as a microgrid, from the main utility grid, and more particularly, selectively disconnecting a power generation source in response to power disruptions or instability.
2. Description of the Prior Art
It is known in the prior art to provide management of power generation or supply including its connection to a power grid for energy distribution, including systems and methods for management of power generation for microgrids, and more particularly to systems related to disconnection of a power generation source from the main power grid, especially in the case of power disruption or instability, methods for detecting power disturbances and disconnecting a power generation source from the power grid, and methods for disconnection of a microgrid or power generator source from the main power grid in response to detection of power disruptions or instability. Many of these prior art documents are specifically related to islanding detection and anti-islanding protection.
By way of example the following are relevant prior art documents for power generation distribution supply management including disconnection of power generation from a grid supply system, consider the following:
U.S. Pub. No. 2004/0252525 for “Method and apparatus for disconnecting an electrical generator from the electricity supply” by inventors Aldridge, et al., describes a controller for disconnecting an electrical generator from the single phase domestic energy supply, wherein the controller includes: means for determining whether the frequency of the single phase domestic electricity supply falls outside a predetermined range; means for determining whether the rate of change of frequency of the single phase domestic electricity supply falls outside a predetermined range; means for determining whether the voltage of the single phase domestic energy supply falls outside a predetermined range; and means for disconnecting an electrical generator from the single phase domestic electricity supply if any of the measured parameters are outside of a predetermined range.
U.S. Pat. No. 7,834,479 and U.S. Pub. No. 2008/0278000 for “Methods and systems for intentionally isolating distributed power generation sources” assigned to Beacon Power Corporation, describe a method for operating a mini-grid including one or more power generation sources and one or more loads connected to a bus, including the steps of: monitoring a condition of a utility grid; disconnecting the mini-grid from the utility grid to operate the mini-grid independently in response to a power disruption over the utility grid; monitoring at least one of a frequency and voltage of power on the bus; and providing an interconnect device connected to the bus, the interconnect device including at least one of an energy storage device and a power quality compensator.
U.S. Pat. No. 7,840,313 and U.S. Pub. No. 2008/0179966 for “Grid interconnection device, grid interconnection system, and electric power control system” assigned to Sanyo Electric, describe a grid interconnection device that converts electric power from a power supply device into predetermined alternating-current power and interconnects the power supply device to a power distribution system, the grid interconnection device including: a detector configured to detect islanding of the power supply device; a receiver configured to receive power failure information including local area information indicative of an area in which a power failure occurs; and a determination unit configured to determine whether or not local area information contained in the power failure information is different from local area information indicative of the interconnected power distribution system, wherein the system is configured to perform power system separation from the power distribution system so as to prevent islanding when the detector detects the islanding state.
U.S. Pat. No. 7,898,112 and U.S. Pub. No. 2009/0146505 for “Apparatuses and methods to connect power sources to an electric power system” assigned to Tigo Energy, Inc., disclose and teach an apparatus having a first connector to interface with a distributed energy source; a second connector to interface with an electric power system; at least one switch coupled between the first connector and the second connector; at least one sensor coupled with the switch; and a controller coupled with the at least one switch, the controller to use the at least one switch to selectively connect or disconnect an electric path between a first connector and second connector based on signals from the sensor; wherein after opening the switch in response to an output of the distributed energy source being outside a predetermined range, the controller is to hold off a period of time according to a set of rules and constraints prior to resetting.
U.S. Pat. No. 6,219,623 for “Anti-islanding method and apparatus for distributed power generation” assigned to Plug Power, Inc., describes an anti-islanding apparatus for isolating a power source from a failed electrical grid, including a power converter to connect the power source and the grid; a means for measuring a voltage of the grid; a means for calculating a voltage trend in the grid voltage, using a present grid voltage measurement and a prior grid voltage measurement; a means for calculating a positive feedback power converter control signal based on the voltage trend; a control circuit connected to the power converter, wherein the control circuit applies the control signal to the power converter; and a means of disconnecting the power source from the grid when the present grid voltage is outside pre-defined limits.
U.S. Pat. No. 7,427,815 and U.S. Pub. No. 2008/0238215 for “Method, memory media and apparatus for detection of grid disconnect” assigned to General Electric, teach a method for preventing islanding in a power system that includes a power grid having a feeder connected in circuit with a distributed generator and at least one load, including the steps of: determining the phase shift of a voltage based solely on sequential frequency measurements at an output of the distributed generator; comparing the phase shift to a threshold phase shift that signifies a phase shift due to a disconnect of the grid from the feeder; and if the phase shift is greater than the threshold phase shift, issuing a command for a disconnect of the distributed generator from the feeder.
U.S. Pat. No. 7,138,728 and U.S. Pub. No. 2003/0080741 for “Anti-islanding techniques for distributed power generation” assigned to Youtility, Inc., describe an anti-islanding system for distributed power on a grid, having a distributed power source operatively coupled to a grid and adapted with output current control, the distributed power source for providing power; a voltage sensor connected to a node between the distributed power source and the grid, and adapted to monitor grid voltage; a contactor operatively coupled between the distributed power source and the voltage sensor, and adapted for disconnecting the grid from the distributed power source; and an anti-islanding protection controller operatively coupled to the distributed power source to selectively output a current pulse in the power being provides so as to cause a voltage deflection in the grid voltage if an island condition exists, and to detect and island condition based on voltage deflection data provided by the voltage sensor wherein the current pulse is requested by the anti-islanding protection controller according to a pre-defined routine depending on the voltage deflection data provided by the voltage sensor.
U.S. Pat. No. 6,815,932 and U.S. Pub. No. 2002/0060556 for “Detection of islanded behavior and anti-islanding protection of a generator in a grid-connected mode” assigned to Capstone Turbine Corporation, teach a method of controlling a generator system connected to an electric power system including the steps of: measuring an output frequency characteristic of the generator system; estimating a first phase angle and frequency of the measured frequency characteristic using a first phase locked loop having a first bandwidth; estimating a second phase angle and frequency of the measured frequency characteristic using a second phase locked loop having a second bandwidth greater than the first bandwidth; calculating a frequency difference between the first and second estimated frequencies; calculating an angle variation that is proportional to the calculated frequency difference; adding the estimated second phase angle and the calculated angle variation so as to form an output current phase angle reference; and controlling an output current phase angle of the generator system to be aligned with the output current phase angle reference; additional steps include determining whether or not the generator system is within a generation island based on the measured frequency characteristic, and stopping the generator system from delivering electric power to the electric power system if the generator system is determined to be within a generation island.
By way of example the following are relevant prior art documents relating to power management: U.S. Pat. No. 7,115,010 and U.S. Pub. No. 2004/0051387 for “Control of small distributed energy resources” assigned to Wisconsin Alumni Research Foundation, describe and teach a microsource system for providing power in an isolation mode or in a grid mode that is configured to couple to a power system without modification of the existing equipment in the power system, wherein the microsource system is configured for use in a microgrid, and wherein the microsource power source may be a fuel cell, a microturbine, battery, or photovoltaic cell.
U.S. Pat. No. 7,983,799 and U.S. Pub. No. 2011/0118885 for “System and method for controlling microgrid” assigned to General Electric, disclose and teach a system for controlling a microgrid including microgrid assets, with at least one of the microgrid assets comprising a different type of electrical generator than an electrical generator of another of the microgrid assets; a tieline for coupling the microgrid to a bulk grid; and a tieline controller for providing tieline control signals to adjust active and reactive power in microgrid assets, and further describes that the electrical generators comprise at least one renewable energy source.
U.S. Pat. No. 7,834,479 and U.S. Pub. No. 2008/0278000 for “Methods and systems for intentionally isolating distributed power generation sources” assigned to Beacon Power Corporation, disclose and teach a method for operating a mini-grid including one or more power generation sources and one or more loads connected to a bus. The method includes the steps of: monitoring a condition of the utility grid; disconnecting the mini-grid from the utility grid to operate the mini-grid independently in response to a power disruption over the utility grid; monitoring at least one of a frequency and a voltage of power on the bus; and providing an interconnect device connected to the bus, the interconnect device including at least one of: an energy storage device for absorbing or releasing real power to control the frequency of the power on the bus, and power quality compensator for absorbing or releasing reactive power to control the voltage of the power on the bus.
U.S. Pub. No. 2007/0040382 for “Self-supporting power generation station” by inventor Towada, teaches a scalable microgrid for providing power to areas remote from the existing power grid, wherein the microgrid comprises at least two power pods linked in parallel, and each power pod has at least one micro-turbine fueled by methane gas, and wherein additional power pods may be added as power needs increase.
By way of example, relevant documents relating to power management and optimization include: U.S. Pub. No. 2009/0062969 for “Hybrid robust predictive optimization method of power system dispatch” assigned to General Electric, describes a system for controlling and optimizing operation of a microgrid by integrating power generation, load and storage assets; it also describes a predictive algorithm that is used to dynamically schedule different assets, the predictive algorithm optimizes the microgrid operation over a predetermined time horizon based on predicted future microgrid asset conditions.
U.S. Pub. Nos. 20100179704 and 20110035073 for “Optimization of microgrid energy use and distribution” assigned to Integral Analytics, Inc., describe a system for optimization of energy use and distribution within a microgrid system, including forecasting of individualized demand by end-use or individualized demand by location for at least one customer or customer location, wherein forecasting of individualized demand may include inputs including: load prediction, weather forecast, risk given load uncertainty; customer compliance forecasts, customer probability of override forecasts; time of day effects; and day of week effects.
U.S. Pub. No. 2010/0222934 for “System for managing energy at loads” by inventors Iino, et al., teaches an energy management system comprising a demand prediction unit configured to predict demand at a load to which energy is supplied and a load adjustment range prediction unit to predict a load adjustment range by using historical data, wherein the system is applied to a microgrid capable of performing demand-side management.
U.S. Pub. Nos. 2011/0082596 for “Real time microgrid power analytics portal for mission critical power systems” and 2011/0082597 for “Microgrid model based automated real time simulation for market based electric power system optimization”, each assigned to EDSA Micro Corporation, describe a system for real-time modeling of electrical system performance of a microgrid electrical system, wherein predicted data for the electrical system is generating using a virtual system model, and the virtual system model is updated based on real-time data to forecast the cost of operating the microgrid and the reliability and availability of the microgrid system.
Furthermore, in relevant art, it is known to describe how energy pricing is integrated into the described forecasting models. By way of example of relevant prior art documents, consider the following: U.S. Pub. Nos. 2011/0082596 for “Real time microgrid power analytics portal for mission critical power systems” and 2011/0082597 for “Microgrid model based automated real time simulation for market based electric power system optimization”, each assigned to EDSA Micro Corporation, teach a system for real-time modeling of electrical system performance of a microgrid electrical system, wherein predicted data for the electrical system is generating using a virtual system model that is updated based on real-time data to forecast the cost of operating the microgrid and the reliability and availability of the microgrid system. Furthermore, all transactions between the public electric service on the macrogrid and the microgrid infrastructure are closely monitored, and rate and pricing information for the management of electricity exchange are also maintained. Closely monitoring this information and updating the virtual and real time models accordingly allows the systems and methods disclosed herein to optimize energy consumption to meet various objectives of the microgrid operator, wherein predicted data can be used to generate market-based pricing predictions based on the performance of the components of the electrical system.
U.S. Pub. Nos. 2008/0262820 for “Real-time predictive systems for intelligent energy monitoring and management of electrical power networks” and 2009/0063122 for “Real-time stability indexing for intelligent energy monitoring and management of electrical power network system”, each assigned to EDSA Micro Corporation, teach the following: the '820 publication describes a system for intelligent monitoring and management of an electrical system including a data acquisition component to acquire real-time data from the electrical system; a power analytics server comprising a real-time energy pricing engine connected to a utility power pricing data table and configured to generate real-time utility power pricing data, a virtual system modeling engine to generate predicted data output for the electrical system, an analytics engine configured to monitor the real-time data output and the predicted data output of the electrical system, a machine learning engine configured to store and process patterns observed from the real-time data output and the predicted data output and configured to forecast an aspect of the electrical system. The '122 publication is a continuation-in-part of '820 and also describes a system for intelligent monitoring and management of an electrical system
U.S. Pub. No. 2010/0198421 for “Methods and apparatus for design and control of multi-port power electronic interface for renewable energy sources” assigned to Board of Regents, The University of Texas System, teaches a method for managing energy movement wherein a determination of whether operational characteristics should be modified is based on at least one factor of: a renewable energy generation forecast, an energy consumption forecast, and a substantially real-time price of energy, with the application of this method and apparatus in a microgrid setting.
U.S. Pat. No. 7,873,442 and U.S. Pub. No. 2006/0206240 for “System and method for managing and optimizing power use” assigned to The Energy Authority, Inc., describe an optimization method for the use of utility power including the steps of: initializing a utility power load requirement forecast, an amount of available utility power, and aggressiveness position for optimizing the use of available power, a utility power schedule; determining an initial power use position for a peak load utility power use range and a low load range; adjusting the utility power use for real-time transactions, adjusting for utility power storage flexibility, and producing a utility power use schedule optimized for use of said utility power in low load range and peak load range, wherein the real-time schedule optimization provides information on how to adjust the use of resources when updated load forecasts based on actual load, and market prices change during the day.
U.S. Pat. No. 7,930,070 and U.S. Pub. No. 2010/0076613 for “System, method, and module capable of curtailing energy production within congestive grid operating environments”, and U.S. Pub. No. 2011/0172835 for “System and method of curtailing energy production within congestive grid operating environments”, each assigned to Kingston Consulting, Inc., describe a method of managing power generation that provides a framework to allow proactive management of alternative energy production through asset monitoring and characterization relative to real-time and anticipated grid conditions, and further describes that the energy management system can perform congestion forecasting, energy output forecasting, proactive curtailments, storage control, dispatch control, real-time pricing, dynamic pricing, or various combinations of features, and a remote monitor and control module that can include on-grid and off-grid control logic, real-time performance monitoring, meteorological data interface, microgrid or asynchronous transmission capabilities, local performance characterization logic, a control panel, or various combinations of features.
U.S. Pub. No. 2011/0093127 for “Distributed energy resources manager” by inventor Kaplan, describes a distributed energy resources manager that connects electrical assets in an electricity distribution grid with other information processing systems to optimize a flow of electric power within the electricity distribution grid.
Further describes that distributed resources may be utilized to meet system-wide needs such as reducing peak consumption, storing excess utility-scale wind or solar power, responding to price signals including real-time or critical peak pricing, or supply ancillary grid services.
U.S. Pub. No. 2011/0071882 for “Method and system for intermediate to long-term forecasting of electric prices and energy demand for integrated supply-side energy planning” assigned to International Business Machines Corporation, describes a method of price forecasting in an electrical energy supply network and/or load (energy demand) forecasting of a given consumer of electrical energy, for identifying the optimal mix of energy hedge and exposure to day ahead/spot market prices for deriving economic benefits in overall energy expenditure; and further describes modeling using real time price and day ahead price data and probability distributions.
U.S. Pat. No. 7,657,480 for “Decision support system and method” assigned to Air Liquide Large Industries, describes a computer-implemented method for identifying an excess energy capacity in a production supply chain by a supply chain operator, in which the supply chain operator also operates at least one power generation facility to sustain industrial production by the production supply chain, the supply chain operator is capable of consuming and selling electricity produced by the power generation facility; and further describes that the forecasted price for electricity during a time period is determined by a forecasting and planning model utilizing historical and real-time data, including the real-time commodity prices for electricity.
U.S. Pat. No. 6,583,521 for “Energy management system which includes on-site energy supply” to inventors Lagod, et al., describes a system for managing the supply of power to a load that receives power from an electric grid, including: at least one on-site power generator that is capable of supplying power to the load independently of the power grid; a controller which processes data relating to at least one factor that is predictive of the reliability and/or quality of power supplied to the load, and selects the power grid or the on-site generator as a preferred power source; and a switch which is responsive to the selection of the preferred power source to connect the load to the selected power source, and further describes that the selection of the preferred power source may be on the basis of relative costs of power supplied via the power grid and the on-site generator; and the relative costs may include data regarding operating costs of the on-site generator, the price of fuel consumed by the on-site generator, and time-of-day pricing (including real time pricing) of power supplied via the power grid.
U.S. Pub. No. 2005/0015283 for “Electric-power-generating-facility operation management support system, electric-power-generating-facility operation management support method, and program for executing support method, and program for executing operation management support method on computer” assigned to Kabushiki Kaisha Toshiba, describes an electric-power-generating-facility operation management support system for determining economically-optimal operational conditions based upon real-time information with regard to the demand for the electric power and the price thereof as well as information with regard to properties of the electric power generating facilities.